Colds, heart disease, even cancer: Why the weather could be to blame
One nutrient is generating excitement in the medical profession: vitamin D.
Low levels of the ‘sunshine vitamin’ have been linked to conditions ranging from colds to heart disease, diabetes, multiple sclerosis and cancer.
Last week, it was reported low levels may be linked to cot death.
In Britain you are unlikely to produce any vitamin D between October and March because the sun is not strong enough and it's often overcast
Yesterday came the news that vitamin D can boost fertility in men and women.
Vitamin D not only helps the body absorb calcium (vital for healthy bones), but also plays a part in the immune system by helping reduce inflammation in the body.
This may explain the link with disease — chronic inflammation is thought to trigger heart disease and cancer. Vitamin D also regulates cell growth, which might explain any possible cancer link.
The Chief Medical Officer is writing to healthcare professionals to advise certain groups — young children, pregnant women, the over-65s and those with dark skins — to take vitamin D supplements.
The problem is that many others might not be getting enough of the nutrient.
Up to a quarter of toddlers may be deficient, according to one study, and a report in the British Medical Journal (BMJ) suggested between a third and half of adults may have inadequate levels.
So how can you tell if you lack this important nutrient — and should you be taking a supplement or just getting outside more We asked the experts…
WHY ARE WE TALKING ABOUT VITAMIN D
It's been well known for years that low levels of the nutrient are linked to weak bones in adults and children. But there has been a spate of studies linking it to a range of major health problems, many of which are on the rise.
These include diabetes — one study last year found obese children with low levels of vitamin D were more likely to develop type 2 diabetes as adults.
Another found adults with low levels had a 57 per cent increased risk of developing the disease.
There could also be a link to the auto-immune condition Crohn’s disease. Researchers found patients may have a reduced ability to absorb the vitamin.
Vitamin D has been linked to cancer. A study in the BMJ showed those with the highest levels of the vitamin in their blood had a 40 per cent lower risk of bowel cancer compared to those with the lowest levels of the vitamin.
Researchers have also suggested a link between vitamin D deficiency and multiple sclerosis. Low levels have even been linked to rheumatoid arthritis.
Then, last week, in a study of babies who died from cot death, pathologists announced moderate to severe vitamin D deficiencies had been found in 75 per cent of the babies.
However, many of the children had underlying condition such as asthma or a viral infection, and the scientists did not compare their findings with the healthy population, so it’s not clear if vitamin D is directly implicated.
CAN I GET ENOUGH FROM FOOD
Sunshine provides 90 per cent of our vitamin D
Sunshine provides 90 per cent of our vitamin D — when heat and ultra-violet light hits the skin, its production is activated.
The main natural dietary sources are liver and oily fish.
Eggs have a small amount and some foods such as breakfast cereals, low-fat spreads, some fresh fruit juices and children’s yoghurts are fortified with vitamin D.
‘However, a serving of a fortified food would give you barely 20 per cent of your daily needs.
'It’s hard to get all your vitamin D needs from food alone,’ says Catherine Collins, principal dietitian at St George’s Hospital, London.
It’s a legal requirement for vitamin D to be added to all margarines and low-fat spreads.
‘However, you would need to eat half a tub of marge a day to get your requirements,’ says Collins.
‘We also adopted the same sun safe message as Australia and America, which was inappropriate, as the intensity of our sunlight is not the same.
So people have avoided going outside without sunscreen and we’ve ended up with a population deficient in vitamin D.
‘The paradox is that studies have found that of people diagnosed with malignant melanoma, the most serious form of skin cancer, those with the lowest levels of vitamin D have the most aggressive forms of the disease.’
SHOULD I WORRY IF I GO OUT A LOT
Virtually everyone in this country will be deficient at some point of the year, says Dr Robert Moy, a Birmingham paediatrician and lead author of a major report on vitamin D.
‘We live too far north and are not assured enough sunny weather to produce adequate vitamin D,’ he says.
Multiple sclerosis, a disease being linked to a deficiency in vitamin D, is most common among people who live furthest from the equator and have least exposure to sunshine.
To make adequate vitamin D, you need regular exposure to the sun during the summer — around ten to 15 minutes daily without suncream between 11am and 3pm, when the sun is hottest.
This isn’t considered a risk for cancer, though you must not allow yourself to burn.
‘The amount of vitamin D you produce depends on how much skin is exposed. Your hands and face are not enough; you need your arms, too,’ says Collins.
In this country you are unlikely to produce any vitamin D between October and March because the sun is not strong enough and it’s often overcast.
Though we can store some, this drops by half within four to eight weeks, so by spring reserves will be gone.
WHO'S MOST AT RISK OF DEFICIENCY
Older people, because the ability to make vitamin D reduces with age. The over-65s are advised to take a 10 mcg daily supplement.
People with darker skin don’t produce the vitamin as easily. Breastfeeding and pregnant women should take a 10 mcg supplement to ensure their children get adequate supplies (it will ensure their immediate bone health and may protect against osteoporosis in later life).
Obese people should also take a supplement, as vitamin D gets locked into fat cells and cannot be used by the body.
Under official guidelines, children between six months and five years old should take a 7 mcg supplement daily, as their bones are going through a critical stage of development.
Lack of vitamin D has led to a surge in cases of rickets.
There is no official advice for older children.
HOW CAN I TELL IF I LACK VITAMIN D
Bone pain, weak muscles or a waddled gait can be a sign of a lack of vitamin D in adults and children.
Another sign in babies is the onset of fits, says Dr Nick Harvey, of Arthritis Research UK, who has helped write official guidance for doctors on a vitamin D blood test.
What’s considered the right level of vitamin D is still not well defined, says Collins. While a reading of 75 nanomoles of vitamin D per litre of blood is said to be enough, some researchers have found 200 nanomoles per litre is needed to improve the immune system.
A two-week winter break in the sun might top you up with vitamin D, but it's not enough to keep you going until spring
SHOULD I WORRY IF I GO OUTSIDE A LOT
Unless you’re in one of the at-risk groups, the jury is out.
‘New studies should help us see if we should all be supplementing with vitamin D and, if so, at what dose and for how long,’ says Dr Harvey.
‘However, with many of these studies we don’t yet know if it’s the levels of vitamin D that cause the condition or if low levels of vitamin D are an effect of them.
‘Also, low levels of vitamin D do not necessarily lead to problems in everyone — many people have low levels and yet have perfectly normal muscle function and no bone problems.
‘I don’t take vitamin D and if you’re white, healthy and active, I don’t think you need one.’
However, other experts take a different approach. Anyone not able to get outside at lunchtime or who does not eat much liver or oily fish should consider taking a supplement, says Collins.
‘I am not in favour of supplements, but I do take vitamin D,’ she says.
‘That’s because I am stuck inside at lunchtime, don’t eat liver and am not keen on oily fish. A pill is easier than trying to get it from food.’
If you do take a supplement, make sure you’re also eating enough fat.
‘Vitamin D is fat-soluble, so will be absorbed only in the presence of fat,’ says Collins.
‘People tend to take their supplements with breakfast, such as a slice of toast or cereal with milk, which is a low-fat meal.
‘U.S. studies have found that people taking vitamin D supplements can double the level in their blood just by taking them before or during their main meal, which tends to consist of more fat.’
For this reason, those on a low-fat diet may be wasting their time taking a supplement.
It takes a month for levels of vitamin D to rise with supplements.
WILL A WINTER HOLIDAY HELP
It’s better to be exposed to the sun little and often, rather than all at once, as we can manufacture only a certain amount of vitamin D at one go.
Once you reach the maximum, your body breaks down the excess, says Collins.
So a two-week winter break in the sun might top you up, but it’s not enough to keep you going until spring.